Tiltable bed with automatic control system

ABSTRACT

A tiltable bed automatic control system for regulation of physiological characteristics such as blood pressure within predetermined limits. For example, the patient&#39;&#39;s blood pressure is continuously measured and monitored through the use of suitable equipment. The magnitude of that pressure selectively actuates the motor of a tiltable platform or bed to appropriately reposition the bed and affect the patient&#39;&#39;s blood pressure accordingly.

United States Patent [191 Toole et al.

[111 3,765,406 14 1 Oct. 16, 1973 1 TILTABLE BED WITH AUTOMATIC CONTROLSYSTEM [76] Inventors: James F. Toole, 1836 Virginia Road; Ralph W.Barnes, Jr., 440 Flynt Valley Drive; Richard Janeway, 2815 Country ClubRoad, all of Winston-Salem, NC.

[22] Filed: Sept. 13, 1972 [21] Appl. No.: 288,719

[52] US. Cl. 128/24 R, 128/1 R, 128/68 [51] Int. Cl A61h 1/00 [58] Fieldof Search 128/24 R, 1 R, 1 B,

[56] References Cited UNITED STATES PATENTS 2,771,069 11/1956 Baron..128/28 5/1962 Cunningham 128/24 R 8/1967' Grosholz et al. 128/1 BPrimary Examiner-Lawrence W, Trapp Attorney-Charles Y. Lackey [5 7]ABSTRACT 11 Claims, 5 Drawing Figures Polygraph Control Unit -l iflENiEnucnsims I 3.7653106 SHEETIUFZ lyqraph FlG.l

l2/ Monitor Control Motor l8 Subject Unit Control FIG.2

34 Preset S stollc Value 3| 45 7 Unit Special Manual 2 36 Rout nesOverride 25 i l Detection of Comparison ,Systolic Errors Table Motion|Table \BlOOd Systolic and to Preset Storage Mom], Plresslire Diastolic ISystolic and Dias tolici5rror Logic Drive npu Blood Pressure DiastolicValues Storage, I 24 g 4O 'lmter Table Derivation Mean BIood ComparisonAngle 30 of Mean Pre of ShortTerm sur ment Blood Pressure smmge and LongTerm Mean Blood Table Pressure 42 Angle v Processing 44 FlG.3

PAlENiEnoct 16m?! 3.765406 sum 2 or 2 Table Motion as a Function ofBlood Pressure Errors Systolic Diastolic Mean Table Error Error ErrorMotion No Error No Error X No Motion Positive No error X Raise head endPositive Positive X Raise head end No error Positive X Raise head end Noerror Negative X Lower head end Negative Negative X Lower head andPositive Negative No error No Motion Positive Negative Positive Raisehead end Positive Negative Negative Lower head and Negative Positive Noerror No motion Negative Positive Positive Raise head and NegativePositive Negative Lower head end Negative No error No error No MotionNegative No error Positive Raise head end Negative No error NegativeLower head end X= Does not matter FIG.4

Systolic high Systolic blood pressure l80 mm Hg Systolic law- Systolicblood pressure g I00 mm Hg Diastolic hlgh Diastolic blood pressure I00mm Hg Diastolic low Diastolic blood pressure S 70 mm Hg Cathetermalfunction Systolic blood pressure MO mm Hg and systolic minusdiastolic .blood pressure 3 20 mm Hg Hypotension Systolic blood pressure5 I00 mm Hg and systolic minus diastolic blood pressure 3 20 mm Hg FlG.5

TILTABLE BED WITH AUTOMATIC CONTROL SYSTEM BACKGROUND, BRIEF SUMMARY ANDOBJECTIVES OF THE INVENTION The present invention relates to atherapeutic device and, more particularly, to a control system fortilting or inclining a bed or platform in order to regulate as much aspossible within limits certain medical conditions of a patient supportedthereon.

Medical science has recognized the value of oscillatory therapy whereina patient is slowly tilted back and forth in accordance with selectedresponses and conditions such as arterial diseases of the lowerextremities, shock, respiratory disturbances involving paralysis ofrespiration, phlebitis, stroke, and others are generally improved. Amost appropriate exemplary application for oscillatory therapy is thecontrol of blood systolic and diastolic pressures by elevating orlowering the patients feet and head as conditions require.

Tiltable platforms or beds have been utilized therapeutically to affector influence patient physical characteristics for many years. Assembliesof this nature are illustrated, for example, in U. S. Pat. Nos.3,200,416; 3,247,528; 3,293,667; 3,392,723; 3,584,321; and 3,609,779.Various control mechanisms for establishing the tilt or incline of thesedevices are well known and include pneumatically operated oscillators,me-' chanically geared elevators, electrical drives and numerousvariations of these components. All of these control systems depend,however, on manual actuation by an operator or patient to mobilize theapparatus and to achieve the desired degree of tilt or incline.

The present invention includes a tiltable bed control system which isautomatically actuated in response to controlling parameters, i.e., thepatient's systolic and diastolic blood pressure, wherein the desireddegree of tilt or incline is automatically established by continuouslysensing and measuring these controlling parameters and determiningwhether or not they fall within predetermined and preselected limits.

Specifically, the control system comprising the present invention isdesigned to adjust automatically the incline ofa tiltable bed orplatform and the supported patient in response to blood pressure valueswhich are monitored continuously by an appropriate sensing device.Desired values of systolic and diastolic blood pressure are measured,and if the patients blood pressure exceeds preset upper pressure limits,the head or upper end of the tiltable bed is raised sufficiently tobring the blood pressure within the preset limits. If the patients bloodpressure falls below lower preset limits, the head or upper end of thetiltable bed is lowered sufficiently to bring the blood pressure backwithin the preset limits. In addition, special procedures areincorporated to minimize excessive motion of the bed or platform and toprovide a series of preplanned motions in response to certainphysiological variables.

From the foregoing, it will be apparent that a primary objective of thepresent invention is to provide a control system of the type describedfor a tiltable surface wherein controlled oscillatory motion of thesurface is completely automated and requires a minimum of manualsupervision.

Another object of the present invention is to provide an automaticcontrol system for a tiltable surface which will cause the surface totilt in a direction that will tend to maintain the blood pressure of apatient within a specified, acceptable range.

Yet another object of the present invention is to provide a controlsystem for a tiltable surface of the type described which can be usedfor therapeutic purposes in any situation where meaningful physicalparameters can be measured and controlled by oscillatory motion of thesurface.

These and other objects of the present invention will become moreapparent after a consideration of the following detailed specificationtaken in conjunction with the accompanying drawings where likecharacters of reference designate like parts throughout the severalviews.

FIGURE DESCRIPTION FIG. 1 is a schematic block diagram of a very basicembodiment of the present invention wherein a tiltable surface isselectively oscillated by directing polygraph blood pressure readings toa control unit which will in turn oscillate the surface withinpredetermined limits in response to the readings obtained from thepolygraph.

FIG. 2 is another schematic block diagram of a more sophisticated systemfor automatically controlling the oscillatory motion of a tiltablesurface wherein blood pressure readings are directed through a controlunit to the appropriate components of the motor directly controlling theoscillatory motion of the tiltable bed.

FIG. 3 is a block diagram of the preferred embodiment of a tiltablesurface automated control system specifically illustrating the basiccomponents and the various overriding and supplemental functions foundnecessary and useful in carrying out the present invention.

FIG. 4 isja table reflecting tiltable surface motion as a function ofblood pressure errors.

FIG. 5 is a table reflecting a number of typical conditions which willgenerate warning signals.

DETAILED DESCRIPTION OF THE DISCLOSURE Referring now to the drawings andparticularly to FIG. 1, a patientlO is positioned horizontally on atiltable bed or surface I2suitably elevated above a working surface 14by an appropriate supporting component 16. A motor 18 is included in thesupporting component to tilt the bed 12 as it is selectively actuated bycooperative elements which will be subsequently described.

A polygraph 20 may be used for monitoring blood pressure of humanbeings. By the use of an appropriate transducer, signals received by thepolygraph can be suitably converted and transmitted to a control unit 22in a form which will selectively activate or deactivate bed motor 18carried by supporting structure 16. By conventional electricalcircuitry, the motor'18 can be driven in one direction when signals ofone nature are received and driven in the opposite direction whensignals of another and decidedly different nature are received.Depending upon the nature of the received signals, the motor 18 can beactivated to inclination of the bed 12 in one direction or another.

FIG. 2 broadly illustrates a relatively simple control systemparticularly designed to regulate the incline of the tiltable bed 12without the use of a polygraph. Here an appropriate electrical responseunit monitors the blood pressure signals received by a conventionalsensing device 24 from the patient, transmits these signals to a controlunit which in turn regulates a motor control unit directly governing theoperation of the tiltable bed motor 18. The monitoring device may beprovided with a display or indicating component 26 for visualobservance, and the motor control unit can be provided with a manualoverride so that an operator or the patient may at any time bypass theregulatory system and control the incline of the tiltable bed at will.

It will be understood that the various units included in the systemsdescribed above are comprised of conventional electric circuitry andcomponents having physical composition and electrical characteristicswhich are well known and consistently within the capabilities of thoseskilled in the art of designing such systems.

FIG. 3 represents the preferred embodiment of the present invention andis directly associated with the control of a tiltable patient-bearingtable in direct response to systolic and diastolic blood pressuremeasurements. While the embodiment is particularly pertinent topatientblood pressure control, obviously, numerous other physicalparameters may be utilized to control the automated system as hereindescribed when motion of the patient can be of therapeutic value.

In FIG. 3, the raw blood pressure data is obtained on a pulse to-pulsebasis from an appropriate sensing device 24 such as an indwellingcatheter 25. From the catheter, the data are fed to systolic anddiastolic peak blood pressure detectors 28 and to a counter 30. Thepurpose of the counter is to obtain blood pressure processing on apulse-by-pulse of every nth pulse, wherein the n can be varied,-forexample, from 2 to 100.

As mentioned, values of systolic and diastolic blood pressure aredetected by peak detectors and compared in a comparing unit 31 to presetvalues of systolic and diastolic ranges manually placed in the systemthrough the use of the preset value unit 34. If the value of detectedblood pressure is within the selected preset values, no error is storedin the systolic or diastolic error storage unit 36. However, if eitherthe detected systolic or diastolic blood pressure or both is not withinthe selected preset values, an error bit is generated. Both positiveerrors and negative errors are stored and summed in the storage unit 38.

The circuitry and components used in this embodiment are designed sothat if there are about 10 positive error bits of the last 12 samples ofblood pressure, a positive error is generated either for systolic ordiastolic blood pressure. Similarly, if there are about 10 negativeerror bits of the last 12 samples of blood pres sure, a negative erroris generated. The errors, if any, for systolic and diastolic bloodpressure are fed to the logic unit 40 for further comparison andprocessing.

A mean blood pressure is derived in the present in- ME? DBP 0.6(SBP-DBP) 0.6 (SE?) 0.4 (DBP) where MBP is mean blood pressure, DBP isdiastolic blood pressure, and SBP is systolic blood pressure.

A short-term mean blood pressure average is obtained by averaging, forexample, the last 12 samples of mean blood pressure. A long-term meanblood pressure is also obtained by averaging, for example, the 96samples of mean blood pressure processed just prior to the short-term 12samples. The value of the short-term average is compared to the value ofthe long-term average in the comparing unit 44. If the two averages arewithin an error bound, no mean blood pressure error is generated. If thetwo mean blood pressure averages are not within an error bound, an errorsignal is generated. A positive error means the short-term mean bloodpressure average is greater than the long-term mean blood pressureaverage.

The systolic blood pressure, diastolic blood pressure, and mean bloodpressure errors, if any, are fed to the bed motion logic unit 40. Twoparameters are checked before any logic operations are allowed to occur.

The first parameter check is to ensure that the systolic blood pressureis greater than an established value, for example, 1 10 mm Hg, and thesecond parameter check is to make sure that the difference betweensystolic and diastolic blood pressure is greater than an establishedvalue, for example, 20 mm Hg. The blood pressure data will be processedif the systolic blood pressure is greater than the established systolicvalue, in this case mm Hg, and the difference between systolic anddiastolic blood pressure is greater than 20 mm Hg. A cathetermalfunction warning signal is generated at a warning unit 45 if thesystolic blood pressure is greater than 1 10 mm Hg, but the differencebetween the systolic and diastolic blood pressure is less than or equalto 20 mm Hg. The catheter malfunction warning signal alerts attendingpersonnel. No further blood pressure processing is done, and no changein the tiltable bed position can occur until the catheter is againfunctioning properly.

If the systolic blood pressure is less than 1 10 mm Hg and thedifference between systolic and diastolic blood pressure is less than orequal to 20 mm Hg, a hypotension warning signal is generated and thesystem enters a hypotension procedure. Attending personnel are alerted,and the tiltable bed enters a special hypotension program describedsubsequently. If the systolic blood pressure is greater than 1 10 mm Hgand the difference between systolic and diastolic blood pressure isgreater than 20 mm Hg, the tiltablebed is in its normal operating mode.

The bed motion as a function of blood pressure errors is given in therepresentative table designated FIG. 4. in that table, the systolic anddiastolic errors are relative to preset values for systolic anddiastolic values, and the mean errors are derived as discussed earlier.For example, if there is a positive error in the systolic blood pressureand no error in the diastolic blood pres sure, the head end of thetiltable bed is raised to lower the blood pressure. The angular volocityof the tiltable bed is of any convenient and reasonable value, butpreferably around 10 per minute or less. This relatively low velocity ispreferred to avoid undue motion sensation by the patient, and to allowtime for physiological adjustment to a new bed incline angle. The bedangle is preferably restricted to lie between +25 and -l2. Beyond theselimits, problems might well arise relating to patient comfort andstability on the bed.

The time duration of the tiltable bed motion is limited in two ways.First, if the blood pressure error disappears, the bed is stopped at theangle where the error disappeared. Secondly, the bed are is preferablydivided into about 8 increments with the horizontal position serving asa reference. The tiltable bed angle is detected by a potentiometerconnected to the pivot point of the table. The analog voltage from thepotentiometer is fed to an A/D converter, which has a change in digitalcode each 4.

The 8 increments in the tiltable table are are chosen for severalreasons. It has been found that a change in the tilt angle of less thanabout 8 does not produce a significant change in blood pressure. Achange in tilt angle of more than about eight degrees produces asignificant change in blood pressure, but the physiological system isnot able to adjust to a change in the tilt angle sufficiently rapidly toprevent an overshoot of the tiltable bed angle in either the positive orthe negative direction.

To prevent excessive over or undershooting of the tiltable bed angle, aspecial routine is activated whenever the tiltable bed angle crosses an8 boundary. When the bed angle crosses an 8 boundary, a change indigital bed angle code is detected, and the bed is automatically stoppedfor about 30 seconds. This allows time for the patients blood pressureto adjust to the new bed angle and to obtain and process blood pressuredata at the new bed angle. At the end of the waiting period, bedoperation is returned to the normal mode of operation describedpreviously.

In addition to the normal mode of operation and the 8 increment routine,two other special procedures are provided. These procedures are referredto as the check routine and the hypotension routine.

The purpose of the check routine is to periodically check the positionof the tiltable bed and to attempt to return the bed near the horizontalposition for the patients comfort. For the positive angles, if the bedangle is greater than about 4, and has remained within an 8 incrementfor a time in minutes selected by, for example, the attending physician,the bed angle is decreased by about 8, with a positive 4 as the lowerlimit. When the bed angle has been decreased for about 8, the tableis'stopped in the new position for approximately 2 minutes. This pauseis sufficiently long to allow adjustment to the new angle and to obtainand process data at the new bed angle. At the end of the waiting period,the bed operation is returned to the normal mode.

For negative angles, the check routine will allow the tiltable bed angleto be less than zero degrees for 2 minutes which is preset in thesystem. At the end of the preset 2 minutes, the table is returned to thezero degree position, and is stopped for 2 minutes. At the end of thewaiting period at zero degrees, the bed operation is returned to thenormal mode.

The hypotension routine is initiated when the systolic blood pressure isless than or equal to an established value, for example, 1 10 mm Hg andthe difference between the systolic and diastolic blood pressure is lessthan an established value, for example again, mm Hg. When this routineis activated, the tiltable bed is returned to the horizontal positionwithout any pauses at the 8 increment or interruptions from the checkroutine. The bed then remains in the horizontal position for 2 minutes.At the end of the 2-minute waiting period, the bed operation is returnedto the normal mode. If the blood pressure is still classified ashypotension, the bed angle is decreased below zero degrees, and thecheck routine is activated as described earlier. The check routine thencontrols the tiltable bed angle. The hypotension and check routinecombination is terminated when the measured blood pressure no longer isclassified as hypotensive at the end of the check routine 2 minutewaiting period at the zero degree position. The bed operation isreturned to the normal mode.

In any mode of operation, a warning system is provided. This systemprovides checks and warning signals when the systolic or diastolic bloodpressure or bed angle exceed certain bounds. A typical set of warningconditions is shown in the table designated FIG. 5. Also included inthis table are the catheter malfunction and hypotension conditions.Warning signals might well be conveyed to attending personnel by, forexample, flashing lights, or other appropriate means.

Several general applications and one specific embodiment of the presentinvention have been described. It is to be understood that theserepresentative examples are not to be construed as a limitation in anyway on the present unique concept. The present invention may well haveapplication in any area where human physical parameters may be utilizedto control, within limits, particular bodily conditions. For example,the invention may be used to control cerebral spinal fluid pressure bysensing the magnitude of that pressure and positioning the bed at anangle to decrease the pres sure. Additionally, cardiac rate may also beregulated with certain limits by, for example, positioning the patientin another relationship if a rapid heartbeat is detected. Otherapplications will be obvious to those skilled in the area of technicalmedicine.

While there has been described an automated control system forregulating a patients blood pressure or other physical characteristics,obviously alterations and variations in the representative examples maybe made without departing from the spirit and scope of the presentinvention. Such changes and improvements are contemplated within thescope of the appended claims.

We claim:

'1. A tiltable bed automatic control system responsive to physiologicalcharacteristics of a patient comprising: a tiltable bed; a tiltable bedmotor; physiological characteristic sensing means; tiltable bed motormeans operable to selectively activate said motor and establish theincline of the said bed and responsive to the output of said sensingmeans whereby the magnitude of the physiological characteristic controlsthe activation of the tiltable bed motor and incline of the bed and thepatients physiological characteristic is held within preset limits.

2. The system as claimed in claim 1 wherein said physiologicalcharacteristic is blood pressure.

3. The system as claimed in claim 2 having manual override meansselectively controlling said tiltable bed motor means to deactivate saidtiltable bed motor and provide manual control therefor.

4. The system as claimed in claim 3, said blood pressure monitoringmeans comprising'a catheter, and said tiltable table motor means furthercomprising checking means to review bed incline for allowable return ofsaid bed to a horizontal position, and hypotensive means regulating bedincline when predetermined blood pressure conditions occur.

5. The system as claimed in claim 1 wherein said physiologicalcharacteristic is cerebral spinal fluid pressure.

6. The system as claimed in claim 1 wherein said physiologicalcharacteristic is cardiac rate.

7. The system as claimed in claim 1 wherein said blood pressure sensingmeans includes discriminating means controlling the operation of saidmotor with respect to preset blood pressure limits.

8. The system as claimed in claim 1 having manual override meansselectively controlling said tiltable bed motor means to deactivate saidtiltable bed motor and provide manual control therefor.

9. The system as claimed in claim 1, said blood pressure sensing meansincluding means monitoring said blood pressure, means establishingselected blood pressure limits, and means comparing the monitored bloodpressure and the selective blood pressure limits, signaling apredetermined dissimilarity therebetween, and storing the dissimilarsignal, said tiltable bed motor means including motor control meansresponsive to the dissimilar signal stored in said comparing, signaling,and storing means.

10. The system'as claimed in claim 9 further comprising mean bloodpressure deriving means, and means comparing sensed blood pressure andderived mean blood pressure for provision to said tiltable bed motormeans.

1 l. The system asclaimed in claim 3 further comprising mean bloodpressure deriving means, and means comparing sensed blood pressure andderived mean blood pressure for provision to said tiltable bed motormeans.

1. A tiltable bed automatic control system responsive to physiologicalcharacteristics of a patient comprising: a tiltable bed; a tiltable bedmotor; physiological characteristic sensing means; tiltable bed motormeans operable to selectively activate said motor and establish theincline of the said bed and responsive to the output of said sensingmeans whereby the magnitude of the physiological characteristic controlsthe activation of the tiltable bed motor and incline of the bed and thepatient''s physiological characteristic is held within preset limits. 2.The system as claimed in claim 1 wherein said physiologicalcharacteristic is blood pressure.
 3. The system as claimed in claim 2having manual override means selectively controlling said tiltable bedmotor means to deactivate said tiltable bed motor and provide manualcontrol therefor.
 4. The system as claimed in claim 3, said bloodpressure monitoring means comprising a catheter, and said tiltable tablemotor means further comprising checking means to review bed incline forallowable return of said bed to a horizontal position, and hypotensivemeans regulating bed incline when predetermined blood pressureconditions occur.
 5. The system as claimed in claim 1 wherein saidphysiological characteristic is cerebral spinal fluid pressure.
 6. Thesystem as claimed in claim 1 wherein said physiological characteristicis cardiac rate.
 7. The system as claimed in claim 1 wherein said bloodpressure sensing means includes discriminating means controlling theoperation of said motor with respect to preset blood pressure limits. 8.The system as claimed in claim 1 having manual override meansselectively controlling said tiltable bed motor means to deactivate saidtiltable bed motor and provide manual control therefor.
 9. The system asclaimed in claim 1, said blood pressure sensing means including meansmonitoring said blood pressure, means establishing selected bloodpressure limits, and means comparing the monitored blood pressure andthe selective blood pressure limits, signaling a predetermineddissimilarity therebetween, and storing the dissimilar signal, saidtiltable bed motor means including motor control means responsive to thedissimilar signal stored in said comparing, signaling, and storingmeans.
 10. The system as claimed in claim 9 further comprising meanblood pressure deriving means, and means comparing sensed blood pressureand derived mean blood pressure for provision to said tiltable bed motormeans.
 11. The system as claimed in claim 3 further comprising meanblood pressure deriving means, and means comparing sensed blood pressureand derived mean blood pressure for provision to said tiltable bed motormeans.